fix: [Search:AppSearch:Engines:Documents page]Customize document sear…

…ch modal dialog missing title from announcement (#202452)

Closes: #202427

## Description
Dialog modal visible title should be announced for the users, especially
using assistive technology to know what dialog modal, flyout opened.

## Changes made:

1. aria-labelledby={modalTitleId} attribute was added for mentioned
EuiModal

## Screen
<img width="1135" alt="Screenshot 2024-12-02 at 14 43 16"
src="https://github.com/user-attachments/assets/ce319c22-1ae9-49e1-99e1-7670e5d97993">

x-pack/plugins/enterprise_search/public/applications/app_search/components/documents/search_experience/customization_modal.tsx

@@ -20,6 +20,7 @@ import {
   EuiModalFooter,
   EuiModalHeader,
   EuiModalHeaderTitle,
+  useGeneratedHtmlId,
 } from '@elastic/eui';
 import { i18n } from '@kbn/i18n';
 
@@ -44,6 +45,7 @@ export const CustomizationModal: React.FC<Props> = ({
   sortFields,
 }) => {
   const { engine } = useValues(EngineLogic);
+  const modalTitleId = useGeneratedHtmlId();
 
   const [selectedFilterFields, setSelectedFilterFields] = useState(
     filterFields.map(fieldNameToComboBoxOption)
@@ -69,9 +71,9 @@ export const CustomizationModal: React.FC<Props> = ({
   );
 
   return (
-    <EuiModal onClose={onClose}>
+    <EuiModal onClose={onClose} aria-labelledby={modalTitleId}>
       <EuiModalHeader>
-        <EuiModalHeaderTitle>
+        <EuiModalHeaderTitle id={modalTitleId}>
           {i18n.translate(
             'xpack.enterpriseSearch.appSearch.documents.search.customizationModal.title',
             {
@@ -132,8 +134,11 @@ export const CustomizationModal: React.FC<Props> = ({
         </EuiForm>
       </EuiModalBody>
       <EuiModalFooter>
-        <EuiButtonEmpty onClick={onClose}>{CANCEL_BUTTON_LABEL}</EuiButtonEmpty>
+        <EuiButtonEmpty data-test-subj="enterpriseSearchCustomizationModalButton" onClick={onClose}>
+          {CANCEL_BUTTON_LABEL}
+        </EuiButtonEmpty>
         <EuiButton
+          data-test-subj="enterpriseSearchCustomizationModalButton"
           fill
           onClick={() => {
             onSave({